The underlying concept behind this proposal is that verbal-cognitive development has its origins in the very early vocal stimulation that the infant receives from the caretaker, and that the effects of such an early stimulation can be detected as early as 3 months of age. In a previous twelve year longitudinal study of 12 male middle SES subjects, the applicant found that 3 month old infants' differential vocal responsiveness (DVR) to their mother versus a stranger under vocal-visual stimulation correlated strongly and consistently with subsequent verbal-cognitive and academic functioning at ages 3, 5, and 12 years. DVR was also related to amount of spontaneous maternal talking to the infant. The objectives of the proposed study are to: 1) Confirm with a broader sample of subjects (n equals 64), including female and low SES subjects, that individual differences in cognitive development can be measured as early as 3 months of age by means of the DVR; 2) Show that, under natural conditions, the individual differences in DVR are related to the amount of interactive vocal stimulation provided by the principal caretaker during the infant's first few months of life; 3) Show that differences in DVR for male vs. female subjects and low vs. middle SES subjects correspond to differences in early vocal stimulation received by these subjects under natural conditions; 4) Show that DVR can be increased by experimentally-induced increased maternal vocal stimulation; 5) Investigate which factors in the infants' early environment, other than direct vocal stimulation by the mother, relate to DVR; 6) Investigate whether there is a salient component to the stimulus which evokes DVR by comparing DVR under vocal-only, visual-only and combined visual-vocal stimulus conditions; 7) Explore whether individual differences in DVR can be detected at age 2 months. Mothers of the experimental group will receive training in mother-infant vocal interaction. All subjects will be visited in their homes for naturalistic observations of mother-infant responses during 3-minute interactions with their mother and a stranger.